Fiber-reinforced polymeric resin composite materials are now widely used due to their outstanding strength to weight characteristics. These characteristics are especially important in the aircraft industry. Currently, structural components of these composite materials are joined to one another or to structural composites of the airframe employing other materials such as conventional metallic fasteners or adhesives. Conventional metallic mechanical fasteners are unsatisfactory for several reasons. They are subject to a weight penalty and are susceptible to galvanic corrosion. Vibrations encountered during normal flight conditions and severe loading as experienced in storms or emergency maneuvers may result in failure of the fastener to the composite structure joint. Adhesively bonded joints cannot be readily disassembled for service and maintenance.
While attempts to solve the aforestated deficiencies have been made using composite plastic fasteners, these earlier efforts have not been widely adopted due to economic or technical shortcomings.
For example, U.S. Pat. No. 3,495,494 to A.L. Scott discloses a threaded plastic member having a glass fiber reinforced thread in which a plurality of resin impregnated glass fiber reinforcing filaments are disposed in serpentine manner throughout the cross section of the thread and extending longitudinally of the axis of the threaded member. Manufacture of the threaded member requires a precision mold having a cavity complementary to that of the member to be formed. According to Scott, nuts may be formed by curing a plurality of resin-impregnated filaments laid axially about a rod having complementary threads and thereafter unscrewing the rod from the molding and cutting the molding into a plurality of nuts. To form the head on a bolt, one of these nuts is screwed onto one end of the shank molding and cemented into place.
U.S. Pat. No. 4,478,544 to Strand discloses a reinforced plastic rivet formed of carbon fibers encapsulated in an incompletely polymerized thermoset resin matrix. To use the rivet, its head portion is heated to soften the resin, the head is upset and fully polymerized. As with all rivets, this one is not threaded. This rivet has the further disadvantage of needing to be stored in a controlled low temperature environment prior to use to prevent premature setting of the resin.
U.S. Pat. No. 2,306,516 to Zahn discloses the use of a parting medium or membrane, such as rubber, over a threaded fastener which functions as a pattern to manufacture a hollow casting mold.
U.S. Pat. No. 4,389,269 to Cooper et al discloses a sport racket frame construction and a method of making same. A resin-impregnated tow is wound about part of a braided tow tube and thereafter a second braided tow tube is placed thereon to form an assembly that is internally pressurized and heat cured.
U.S. Pat. No. 4,265,981 to Campbell discloses impact resisting composites which may comprise multiple parallel filaments helically wrapped by continuous multiple filaments or strips and embedded in a matrix material.
It is evident from the foregoing that a need remains for a threaded composite fastener that may be made economically in the absence of expensive molds and exhibits physical characteristics similar to modern composite materials such as those employed in aerospace applications and in harsh chemical environments.